The San Diego City Council on Tuesday will dive into the touchy topic of reclaiming wastewater for use in a drinking water reservoir.

City staff is asking the council to approve a $6.6 million contract with the global engineering firm Camp Dresser and McKee to design, test and operate a small-scale advanced water treatment plant.

The pilot program won't put re-purified wastewater into a reservoir. Instead, it will test whether the city's proposed treatment system can clean sewage enough to make "reservoir augmentation" an option if the city decides to build a full-scale facility.

Similar concepts have floated around the city for more than a decade but they have faltered partly because of concerns about the reliability of water-cleansing technology. Opponents have dubbed the process "toilet to tap."

The $6.6 million contract is part of an $11.8 million project approved by the City Council in 2007. A rate increase to pay for the project started in 2009.

Environmental groups such as San Diego Coastkeeper have urged their members to attend Tuesday's meeting in hopes of swaying the vote.

"Since San Diego currently imports 80 percent of its water supply, it's essential we find local sources of drought-proof water that are more sustainable and require less energy than increasingly expensive imported water," said a Thursday statement by the nonprofit organization. "Recycling our wastewater will also reduce the 150 million gallons a day that we currently pump into our ocean."